Isaac is strengthening

By: Dr. Jeff Masters , 2:58 PM GMT on August 24, 2012

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Tropical Storm Isaac is strengthening. An Air Force Reserve hurricane hunter aircraft measured surface winds of 60 mph on the east side of the center, about 170 miles south of Santo Domingo in the Dominican Republic, at 8:40 am EDT this morning. Winds at the aircraft's flight level of 5,000 feet were hurricane force, 76 mph. The surface pressure remained fairly high, at 1000 mb. Tropical cyclones have a warm core, and the Hurricane Hunters typically find that a storm's lowest pressure is also where the warmest temperature are. However, this morning's flight found that Isaac was still disorganized, with the storm showing almost no evidence of a warm core. Isaac's warmest temperatures were displaced 75 miles to the west of where the lowest pressure was. There were no signs of an eyewall beginning to build. Infrared and visible satellite loops show that Isaac is somewhat asymmetric, with a large band of intense thunderstorms to the east, separated from the core region. This is interfering with both the storm's low-level inflow and upper-level outflow, but the band appears to be dying out. An analysis of upper level winds from the University of Wisconsin CIMSS shows an upper-level outflow channel well-established to the north, and an intermittent outflow channel to the south.


Figure 1. Evening shot of Tropical Storm Isaac taken on August 23, 2012, by the NOAA Hurricane Hunters.

Isaac's rains
Radar imagery from Puerto Rico shows that Isaac is dumping some very heavy rains to the south and east of the center. Ponce, Puerto Rico had a wind gust of 37 mph this morning as a heavy band of rain moved through, and radar-estimated rainfall amounts are in excess of 7 inches for the region just north of Ponce. Power outages to 2,000 homes have been reported in Puerto Rico this morning. NOAA buoy 42085 offshore from Ponce reported a wind gust of 54 mph near 9 am EDT this morning. Rainfall estimates from microwave satellite instruments suggest that Isaac's heaviest rains are to the south of the center, and that the Dominican Republic and Eastern Haiti will escape the worst of Isaac's rains. Haiti's southwest peninsula and Eastern Cuba should suffer the heaviest rains.


Figure 2. Radar-estimated precipitation from the Puerto Rico radar shows the region near Ponce has received up to 7" of rain as of 10 am EDT August 24, 2012.

Latest model runs for Isaac
The latest set of 00Z and 06Z (8 pm and 2 am EDT) model runs have come into better agreement, thanks to the dropsonde mission by the NOAA jet yesterday afternoon and evening. Isaac should move over Haiti's southwest peninsula and then eastern Cuba, then track along the spine of Cuba before popping off into the Florida Straits on Sunday. A trough of low pressure will then pull Isaac to the northwest, and then north, towards the Central Gulf Coast. Landfall locations range from Mississippi (06Z HWRF model run) to the Florida Panhandle south of Tallahassee (06Z GFDL model run.) It is possible that the trough of low pressure pulling Isaac to the north may not be strong enough to pull Isaac all the way to the northeast and out to sea, and the ECMWF model indicates that Isaac could stall out after landfall over the Tennessee Valley for several days.


Figure 3. Predicted 5-day rainfall total ending at 2 am EDT Wednesday August 29, from Tropical Storm Isaac. Graphics were generated from the 6Z (2 am EDT) August 24, 2012 run of the HWRF model. Image credit: Morris Bender, NOAA/Geophysical Fluid Dynamics Laboratory.

Intensity forecast for Isaac
Isaac has not intensified as much as predicted, and I think that the storm's very large size is partially responsible for that. It's tough to spin up as much atmosphere as Isaac is attempting to do very quickly. Conditions remain favorable for intensification today, with wind shear low, 5 - 10 knots, ocean temperatures warm, 29°C, and dry air mostly mixed out of the storm's core. The large band of intense thunderstorms to the east, separated from the core region, appears to be dying out now, which will help the storm grow more organized. The storm's structure has improved considerably between 9 am - 10 am EDT, with a fairly tight center forming, exposed to view, on the north edge of Isaac's heaviest thunderstorms. A curved band of heavy thunderstorms is now trying to wrap around this center to the northeast, and this band will bring very heavy rains to Haiti and the Dominican Republic this afternoon. I expect that the Hurricane Hunters will observe a partial eyewall in their vortex reports between 2 - 4 pm EDT this afternoon. The storm's large size and disorganized structure suggests that Isaac will be able to intensify only slowly today, and will have top winds of 70 - 75 mph before encountering Southwest Haiti and Eastern Cuba tonight and Saturday. Isaac will likely be a 50 - 60 mph tropical storm on Saturday and Sunday as it moves over Cuba. Once Isaac pops off the coast of Cuba into the Florida Straits, it will be over very warm waters of 31 - 32°C (88 - 90°F), wind shear will be light to moderate. The upper-level wind pattern favorable may be quite favorable for intensification, with low wind shear due to an upper-level anticyclone over the storm--though the models disagree on whether or not this anticyclone will set up directly over Isaac or not. It will probably take at least 24 hours with the storm's center over water for it to become a hurricane. It is possible that Isaac could be approaching Category 3 strength by the time it makes landfall on Tuesday on the Gulf Coast, as suggested by the latest 06Z run of the HWRF model.

Impact on Tampa, Florida
The Republican National Convention begins on Monday in Tampa, Florida. The latest 11 am EDT wind probability forecast from NHC gives Tampa a 17% chance of receiving tropical storm-force winds and a 1% chance of receiving hurricane-force winds on Monday. Tampa is in the NHC cone of uncertainty, though near the edge of it. At a minimum, Tampa will receive very heavy rains and wind gusts in excess of 40 mph. Isaac is going to be hard-pressed to bring hurricane-force winds to the city, though, since any path that takes it close to Tampa would keep the storm too close to land for significant intensification to occur. I put the odds of a mass evacuation being ordered for Tampa during the convention at 1%. I have detailed information on Tampa's storm surge vulnerability in a post from last week.

Invest 97L off the coast of Africa
A tropical wave that moved off the coast of Africa on Thursday has been designated Invest 97L by NHC this morning. The storm has a modest amount of spin and heavy thunderstorms, and is under moderate wind shear of 10 - 20 knots. In their 8 am EDT Tropical Weather Outlook, NHC gave 97L a 30% chance of developing by Sunday morning. The 8 am EDT SHIPS model forecast predicts that 97L will track west-northwest over the next few days, and encounter a region of high wind shear associated with an upper-level low on Monday and Tuesday. This low may be capable of tearing the storm apart, as happened to Tropical Storm Joyce. None of the models currently foresee that 97L will affect the Lesser Antilles Islands, but 97L may pass near Bermuda 7 - 8 days from now.



20th anniversary of Hurricane Andrew
Today, August 24, is the 20th anniversary of Hurricane Andrew, which hit South Florida as a Category 5 hurricane with 175 mph winds--one of only three Category 5 hurricanes ever to hit the U.S. With Isaac churning through the Caribbean this week, I didn't have time to prepare a special post on Andrew, but our Hurricane Andrew archive page has links to satellite and radar images, newspaper headlines, and 49 YouTube videos. Here's an additional link for an Andrew damage video shot by wunderblogger/storm chaser Mike Theiss, when he was 14 years old.

Jeff Masters

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Quoting reedzone:
NHC remains west of the model consensus.. They just don't want to let go of their precious EURO model (kidding), which remains west to Alabama.. Not gonna happen. In time, the track will shift to the east. A storm CANNOT bust into the corner of a building ridge. It's impossible. My opinion, Isaac is unfortunately Tampa bound. I see Isaac hugging the west coast of FL, then recurving as soon as it reaches Tampas latitude.


Ya know what? If I had to bet, I'd bet you're pretty close to right...
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500 mb vort at 42 hrs

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Quoting Grothar:
Starting to look like that worst scenario track for Tampa... just saying. People need to get less complacent around this city...
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Quoting matilda101:
We better just hope that Isaac doesn't pop out on the north side of Cuba earlier than expected as it would have more time to intensify and more issues for the Bahamas, FL Keys, and South Florida


That's exactly what the 12Z GFS is showing. Has Isaac off the north coast of Cuba by 36 hours.
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Quoting oracle28:


The "Village Idiot" userid is already taken, or I would have picked it, instead of oracle28.


We can look for alternative words to susbstitute "Village".... ;)


What about this looks familiar?
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Quoting reedzone:
NHC remains west of the model consensus.. They just don't want to let go of their precious EURO model (kidding), which remains west to Alabama.. Not gonna happen. In time, the track will shift to the east. A storm CANNOT bust into the corner of a building ridge. It's impossible. My opinion, Isaac is unfortunately Tampa bound. I see Isaac hugging the west coast of FL, then recurving as soon as it reaches Tampas latitude.

It's not headed into a ridge. The Euro shows it being forced NW by the Bermuda high.
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205. 7544
if the gfs shows miami landfall this run im going to scream lol looks to be going more north this run so far
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convection firing around center.
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Quoting reedzone:
NHC remains west of the model consensus.. They just don't want to let go of their precious EURO model (kidding), which remains west to Alabama.. Not gonna happen. In time, the track will shift to the east. A storm CANNOT bust into the corner of a building ridge. It's impossible. My opinion, Isaac is unfortunately Tampa bound. I see Isaac hugging the west coast of FL, then recurving as soon as it reaches Tampas latitude.


If that verifies, the check is in the mail, bro. LOL.
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9lL a broad area of low pressure will break off into a northern part which will go wnw and the southern half half which will be the dominant one will move west.
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Quoting reedzone:
NHC remains west of the model consensus.. They just don't want to let go of their precious EURO model (kidding), which remains west to Alabama.. Not gonna happen. In time, the track will shift to the east. A storm CANNOT bust into the corner of a building ridge. It's impossible. My opinion, Isaac is unfortunately Tampa bound. I see Isaac hugging the west coast of FL, then recurving as soon as it reaches Tampas latitude.
..ive been wondering reed IF that could happen..its a worst case possibility because of the pushing the bay waters inland on top of the surge waters from the gulf..this could be historic if it happens
Member Since: August 6, 2011 Posts: 4 Comments: 38197
We better just hope that Isaac doesn't pop out on the north side of Cuba earlier than expected as it would have more time to intensify and more issues for the Bahamas, FL Keys, and South Florida
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One good thing about the XTRAP model is that it can tell you the current heading of a storm... If XTRAP shows a west forecast then that must mean that it is moving west, not Isaac specefic just an example
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Quoting presslord:


Aw, man!!!! That's not fair!!!! I wanna be the Village Idiot!!!!!
Being that this is an election year, we should nominate a village idiot, and vote accordingly. There will likely be very few exceptions of those that will qualify.

Isaac's westward progress appears to be slowing, the turn may be close if it hasn't already started.
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Quoting seafarer459:
XTRAP. The most misunderstood and under loved model ever.
I thought it was FLANALF
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Quoting yoboi:
how many peeps from fla in here???


Sitting Patiently in St Petersburg, On the water.
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Member Since: July 17, 2009 Posts: 71 Comments: 26037
Quoting presslord:


Aw, man!!!! That's not fair!!!! I wanna be the Village Idiot!!!!!


The "Village Idiot" userid is already taken, or I would have picked it, instead of oracle28.

On a serious note, could the interaction with the islands, be pulling Isaac northward, due to frictional drag?
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Report and move on. Don't quote stupidity.
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Quoting presslord:


Aw, man!!!! That's not fair!!!! I wanna be the Village Idiot!!!!!
LMAO!!
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NHC remains west of the model consensus.. They just don't want to let go of their precious EURO model (kidding), which remains west to Alabama.. Not gonna happen. In time, the track will shift to the east. A storm CANNOT bust into the corner of a building ridge. It's impossible. My opinion, Isaac is unfortunately Tampa bound. I see Isaac hugging the west coast of FL, then recurving as soon as it reaches Tampas latitude.
Member Since: July 1, 2008 Posts: 13 Comments: 7365
Big rain coming now!:)
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Quoting SFLWeatherman:

..amazing amounts of water these things can dump on you..remember folks..1 inch of rain equals 1.2 feet of rain per acre on the ground..now 8+ inches of rain..and could be alot more than that..think about the streams and ponds and lakes near you..whew..this no matter the winds..is going to be a flooding event..and the people in PR are saying this storm has tons of rain in it.
Member Since: August 6, 2011 Posts: 4 Comments: 38197
On the weather channel, sidell is in cuba and abrams in the key west.

Abrams was talking to the mayor of KW and they said they don't evacuate unless Cat 3 or higher.

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33 hrs

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Quoting opal92nwf:
When was the last time someone saw a hurricane landfall in North Korea?


They call them "Typhoons" over there, and it was probably during the past year or two.

They get hit every few years, and S. Korea gets hit more often.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
500 mb vort a 24 hrs. this is the steering.

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XTRAP. The most misunderstood and under loved model ever.
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183. FOREX
Quoting Elena85Vet:
What's all that scurrying about noise coming from the dirrection of Panama City, FL?



huh???
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Quoting CJ5:


Please stop. You do this every day and no one thinks it funny. You are the village idiot, just go away.


Aw, man!!!! That's not fair!!!! I wanna be the Village Idiot!!!!!
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It is near impossible to forecast an intensity at this point. Upper levels, ocean temperatures, and time over water can support up to a cat 5. But Isaac might never completely consolidate its core and never make it to hurricane status. You throw in some land interaction and it's near impossible to make an accurate intensity forecast.

Isaac could be another Katrina, Ike, or TS Debby from this year.

Prepare for the worst and hope for the best because in 5 days, there is no telling what we're going to have on our hands.
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Quoting 12george1:

XTRP is that model that shoots west-southwestward into Central America and is totally an outlier.

it is not a model. it shows the direction the storm was heading and where it would go if it kept going in a straight line on that heading. it will show WNW next time it updates.
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Quoting FOREX:


Anyone familiar with the topography of the part of Cuba Isaac will spin over? Will it run into the highest peaks or go West of them???


The highest mountains are in the SE corner of Cuba.

The highest peak is 6500ft, the rest ave 4500ft or so.

If Isaac follows the current NHC track he will cross the mountains.
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Quoting FOREX:


Anyone familiar with the topography of the part of Cuba Isaac will spin over? Will it run into the highest peaks or go West of them???


According to this Isaac will be traveling over the flattest part of Cuba..

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24HR GFS:

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Quoting cgthms:
XTRAP is not a model . It just shows the direction the storm is moving at that given moment.


Oi vey, I applaud thee.
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Quoting HurricaneDean07:

I believe the NHC needs to be upping the Intensity when Isaac gets through with the Islands... QUICKLY.
The Gulf Coast could easily get cuaght off-guard with the NHC forecasting a Category 1, and yet Isaac could go through RI in the Eastern Gulf and become a Category 3.
Yea...I was just at Home Depot in Naples and there is only a handful buying plywood. No gas lines. Seems everyone thinks it's going right on by.....oh well. I filled my tanks. Have over 40 gal gas ready for generator too.
Could be a rude awakening come Sunday....

Just helped tie up friends Hatteras at the marina. We have over 20 lines springing...
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Wow, Doc says "approaching Cat 3". That IS a difference maker.

I gased up the autos this a.m. Most of my neighbors and last night's Mobile news interviewees of locals were calling this 'just a big thunderstorm.'

In my opinion, I think when it pops out after Cuba, assuming it is moving slow enough to actually intensify, many many people around here in Baldwin County / Mobile Bay / Gulf Shores will be very suprised.

Monday will be a wakeup call around here I think...
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WOW 97L going to the USA???
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It will probably take at least 24 hours with the storm's center over water for it to become a hurricane. It is possible that Isaac could be approaching Category 3 strength by the time it makes landfall on Tuesday on the Gulf Coast, as suggested by the latest 06Z run of the HWRF model.

Thanks Dr. M; that remains the million dollar question and the greatest weakness in tropical storm intensity forecasting...........Time for folks from the Northern Gulf coast to Florida (certainly the Keys and West Coast)to take this storm very seriously and to start looking at your preparation plans this weekend in case he ramps up on short notice.
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Quoting TampaFLUSA:

You're being sarcastic, right?

XTRP is that model that shoots west-southwestward into Central America and is totally an outlier.
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Quoting Maineweatherguy20023:

SAD back to ISAAC now


LMAO
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Guys the new GFS will only give me a one day look right now BUT..look where issac is..IS it possible..issac sneaks up inbetween those two islands?
Member Since: August 6, 2011 Posts: 4 Comments: 38197
Quoting weatherguy03:
Levi and I were talking about this on FB last night on the strange direct track NW through the Eastern GOM and why there wasnt more of a bend off to the North and NE later in the track. Well you can see the first run 12Z models starting to show that bend. Makes more sense to me.

I called for this yesterday morning lol... the models have been showing the hook getting further and further south
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Quoting ncstorm:
Were the waters in the GOM the same temp when Debby went through??..its not about temps in the GOM that intensify a storm..there are many other variables that come into play
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What's all that scurrying about noise coming from the dirrection of Panama City, FL?
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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